ISP Wireless - Device with LAN Connectivity or Ethernet Issues

This article includes the basic troubleshooting steps for devices without LAN management access,  failing Ethernet connections, or Ethernet negotiating at lower rates. Also includes information related to failed Ethernet connections on airFiber devices resulting from FCS errors.

Symptoms & Steps to Troubleshoot

Symptoms: Device has no LAN management access; intermittent/failing Ethernet; Ethernet negotiating at lower rates.


  • Can access via RF interface or management radio (if applicable)
  • Can not get LAN connection via switch or router port.
  • Can not discover radio.

Symptom Troubleshooting Steps

1. Is your Ethernet run longer than 100 meters?

  • Yes: Cables must be equal to or less than 100 meters long. Any longer and the cable no longer fits the Ethernet standard. POE devices are even more bound by this standard due to the voltage drop on longer cables. The longer the cable, the less voltage you will see at the far end of the cable, providing less power to the device that is being powered via the cable.
  • No: Continue to step 2.

2. Are you using shielded Ethernet cables? (e.g., TOUGHCable)

  • Yes: Continue to step 3.
  • No: Shielded Ethernet Cable is a requirement. TOUGHCable or equivalent should be installed.

3. Reboot the device.

  • If rebooting solves the negotiation issues, monitor the ethernet link.
  • If negotiation issues reemerge, Continue to step 4.

4. Plug directly into PoE Injector LAN port.   

  • Do you get a LAN connection on your computer?
    • Yes: Try a different switch port. Done!
    • No: Continue to step 5.

5. Replace POE injector.

  • Do you get a LAN connection on your computer?
    • Yes: Dispose of the damaged PoE injector. Done!
    • No: Continue to step 6.

6. Swap the short jumper cable that runs between the PoE Injector and the computer.

  • Do you get a LAN connection on your computer?
    • Yes: Dispose of the damaged short ethernet jumper.
    • No: Continue to step 7.

7. Swap the ethernet cable between the radio and POE injector.

  • Do you get a LAN connection on your computer?
    • Yes: Make sure your new cable is properly installed, terminated, and secured.
    • No: Continue to step 8.

8. Is this device colocated on a mast with an FM transmitter?

  • Yes: There is a strong possibility of line interference. This is caused because FM transmitters operate on close to the same frequency of the Ethernet cables themselves. Isolate the radio from potential EMI sources or use ferrite beads with shielded Ethernet cables.
  • No: Continue to step 9.

9. If all else fails, replace the device with a known working device, and double check cable termination and grounding.

Symptoms: FCS Error counter rising on the switch port connected to airFiber device.

Symptom Troubleshooting Steps:

FCS errors can be caused by a few different factors:

  • Most commonly, the issue is management frames being sent over the wireless interface.
    • The airFiber team already addressed a software issue, resolved by updating to the latest available firmware versions on the Releases page.
    • Most older reports of FCS errors stem from this, and do not affect customer traffic.
  • Failing POE or Ethernet cable, or a low-quality Ethernet cable.
    • Replacing the cable and/or the POE has solved the FCS errors for many customers in the past.
    • Check PoE AC power source.
  • Energy coupled into Ethernet cable from RF or magnetic sources.
    • Is cable located in a high RF environment and shielded/grounded properly?
  • Inline lightning protection devices
    • Bypass the device to determine if the FCS issue is resolved.
  • Failed/failing Ethernet port on the device itself.
    • This is caused by improper grounding practices during the installation and maintenance of the AF24/HD. 

A few things that can help:

1. Following proper ground recommendations. Follow the grounding recommendations in this guide.

2. Reduce the length of the Ethernet run. This can be difficult to overcome; Ubiquiti offers two devices that can help:

3. Install Ferrite choke on both ends of the Ethernet run.

4. If all else fails, replace the radio with a known working radio, and double check cable termination and grounding.

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